Drying lumber.



A. D. LINN.

DRYING LUMBER. APPLIGATIOH FILED APR. 10, 1908.

4 SHEETS-SHEET 1.

; WITNESSIS: v INVENTOR:

I 'ifii w. ATTORNEYS.

Patented 0ct.10,1911.

A. D. LINN.

DRYING LUMBER. APPLICATION FILED APR. 10, 1908.

4 SHBETS-SHEYET 2.

WITNESSES: INVENTOR: 0? w '8. 414.,

BY X%%MQ% ATTORNEYJ.

' Patented Oct. 10, 1911.

A. D. LINN. DRYING LUMBER. APPLIGATIQN FILED APR. 10, 1908 1,005,243, Patented Oct. 10, 1911.

4 SHEETSSHEET\3.

ITNESSESI -z INVENTOR'. I Q wazza,

BY 1 4mm? Wm 4 ATTORNEYS.

A. D. LINN. DRYING LUMBER. APPLICATION FILED APB. I0, 1908.

Patented Oct. 10, 1911.

4 SHEETS-SHEET 4.

MENTOR: 4'9. 314

BY W- r/ww x, ATTORNEYQ.

@ESS

UNITED STATES" PATENT orrrca.

ALLEN D. LINN, OF GRAND RAPIDS, MICHIGAN.

DRYING LUMBER.

Specification of Letters Patent.

Patented Oct. 10, 1911.

Application filed April 10, 1908. Serial No. 426,235.

oughly dry lumber, intended for use mainly under conditions requirin non-shrinking qualities, as, for instance, in the manufacture of furniture, h'ouse trimmings, and the like. The purpose proposed is attained without damage to the wood from checking, scaling, hardening, honey-combing, souring or cracking; and, in a relatively short time, having in view the necessity for maintaining, throughout the operation, certain safeguards, indispensable to its full efiiciency.

The generic features of my invention are applicable both to single compartment or box kilns and to multiple compartment or progressive kilns, as will hereinafter mor fully appear, although specifically the operation in the two cases exhibits points of difference appropriate to minor variations in the conditions prevailing.

In the accompanying drawings, Figure 1 represents a vertical longitudinal section on the line 1-1 of Fig. 2, of a kiln appropriate to the practice of my invention; Flg. 2represents a horizontal longitudinal section and partial plan view of the same, certain portions of the heating pipes being shown as broken. away, for clearness of illustration; Fig. 3 represents a transverse section, on the line 33 of Fig. 2, and'Figs. 4:, 5, 6and 7 represent on a larger scale certain preferred details of construction.

Similar letters of reference indicate similar partsthroughout the several views.

Referring to the drawings, A indicates the side walls of the kiln, and C indicates the end walls provided respectively with the entrance door a and exit door 5.

0 indicates the ventilating or draft discharge flues, projecting through the roof B;

and provided with horizontal extensions or intakes c, which rest upon the floor D of the kiln and which are provided with hinged valves or shutters d and with slide dampers e. The ventilating or draft discharge fiues c are furthermore provided with suitable outlets'ol and each contains a steam pipe or bend provided with the usual automatic air vent or pet cock at the top of each 'bend, said air vent being of any type usually employed in steam radiator systems. The up-going leg of each of the loops communicates with the steam supply pipe f and the down-going leg of each loop'connects with the common return or drip pipe 7. The steam supply pipe f is connected by a branch to the main steam supply pipe H and the quantity of steam entering the supply pipe f is regulated by means-of a suitable valve operated by the stem f so that the amount of steam passing through the return loops in the several ventilating or draft discharge flues 0, and consequently the .drawing power of said fiues, may be appropriately dfetermined to suit the varying exigencies 0 use.

As shown more fully in Figs. 5 and 6, the

valves d may conveniently be flaps, fixed upon a rotary valve stem d having an operating handle 03 and the dampers 6 may conveniently be slide valves operated by a stem '6 having an operating handle 6 (see Fig. 1). By the appropriate manipulation of the rotary valve stem cl and the valve stem 6 the area of the inlet openings of the branches 0 of the ventilating or draft discharge flues can be adjusted with great accuracy, and the openings controlled by the hinged valves d and dampers cmay be absolutely closed, when desired.-

' It will be noted that the kiln is separated by a solid dividing partition F and a drop curtain or door G into two compartments, and that the ventilating or draft-discharge flues of the forward compartment, are provided with valve operating stems which are independent of the like valve operating stems of the rear compartment, for purposes hereinafter to be more fully described.

In order to prevent the curtain G from moving or curving inwardly or outwardly, which is liable to occur with hanging curtains under different conditions of pressure in the two compartments, I provide, at each end of the curtain, an inchned supporting guide rail g, upon which the ends of the in the form of a return loop curtain roller 9 may move up and down, as illustrated more fully in Fig. 4. I also provide the curtain in the usual way with operating Cords g 9 passing over suitablevertical, and thecurtain is sufliciently heavy,

to closely maintain its position against the guide rails as against any pressure that may normally arise within the kiln on either side of the curtain. The partition F, immediately below the curtain, extends entirely across the kiln from side wall to side wall thereof, and isimperforate, save for apertures through which pass snugly the pipes of the steaming apparatus.

The forward header E of the steaming apparatus, supplied from the inlet pipe H is provided with a set of imperforate steam pipes 71. which extend from endv to end of the kiln and which are connected at their outlet ends with the discharge header E, from which the water f condensation is taken off to the disc 3e ipe a to be returned, if desired, ton 1e eed water heater of .the steam generator, together with the condensation from the pipe F.

In the forward compartment of the kiln there are arranged immediately above the steam heating pipes n thereofsteam spray pipes m having perforations or sprayingapertures, as shown. These steam spray plpes are connected, as shown more fully in Fig. 7, with the main steam supply pipe H and are each provided with regulating valves having operating handles m, so as to approprlately diminish or increase the amount of steam sprayed into said compartment. So also, the rear compartment ofthe kiln is provided at a point proximate to the-curtain with like spray pipes m supplied from the main pipe H and having a regulating valve independently operated from the stem m ,"so that the two sets of spray pipes m and m may be under separate control.

In the front compartment of the kiln and opposite the wall containing the draft discharge flues 0 are located the vertical flues s which communicate freely at their upper ends with the interior of' said compartment and which communicate at their lower ends with the air intake flue 8'', adapted to be closed or opened to the extent desired by the slide 25 (see Fig. 7 partment of the kiln is provided with hke vertical flues s and with a like air intake flue 8 having a similar air inlet controlling slide, not shown. The cars upon which the lumber to be dried .is piled are adapted to run upon the rails 4) which are suitably supported upon the standards and foundation So also, the rear compillars shown, arranged in such proximity to each other as to give the track rails substantial support.

In drying lumber, in accordance with my invention, I may conduct the entire operation in a single compartment, as, for instance, by throwing both of the compartments of the kiln shown in the drawings into one by raising the dividing curtain or partition, thereby converting it into a socalled box kiln. I will accordingly first describe the 5 steps pursued when the entire treatment is in a single compartment box kiln, assuming, for purposes of illustration, that the dimensions thereof are, say seventeen and one-half (17%) feet in width; fiftyone (51) feet in length, and nine (9) feet in height. In such a kiln, the heating pipes a may conveniently be about one foot below the cars upon which the lumber is piled, and the steam spraying pipes may be substantially intermediate between the car rails and the steam heating pipes 02, and the heating pipes themselves, one inch in diameter, are preferably present in the ratio of five (5) feet of heating pipes for each square foot of floor surface. A box kiln of this character is well adapted for instance for the eflicient drying of oak lumber, one inch thick and which has been air dried in the usual way for a period of, say, six months. In giving this illustration of the practice of my invention, I will assume that the temperature of the kiln before the introduction of the lumber is about 75 F., and that the exterior of the kiln has the ordinary summer temperature of from 80 F. to 90 F.

Steam is first blown through the heating pipes n and spraying pipes m, m, to remove any condensation therein and to raise the.

temperature of the, said pipes to a degree sufficient merely to prevent them from acting as condensers. The steam employed may be either live steam or exhaust steam. It is preferred to use very low pressure live steam, since, in using exhaust steam the conditions vary at different times, making it diflicult \to maintain an even pressure. A pressure of about two pounds is all that is desiredthe lower the better, so long as the pressure is even and sufficient to produce the spray. I

The cars of lumber are then introduced into the chamber and all doors and valves are closed, so that the interior is as air-tight as may be with kilns of this type, which are usually built at least in part of wood, so that it is impossible to make them absolutely air-tight. I then turn on the steam into the heating pipes and the spray-pipes and fill the interior of the compartment with the sprayed steam. The steam spray is continued for three or four hours, and to a degree sufiicient to .run the humidity up as quickly as possible to from 80% to 85%, or as near thereto as is attainable, the temperahas been turned on, the surface of the'lumher will have attained approximately the same temperature as the surrounding vapor,

i. 6., 130 F. to 140 F. At this point, I

gradually admit additional steam into the heating pipes, and thereby gradually raise the temperature in the chamber to approximately 150 F. This gradual increment of the temperature will extend over a period of about twenty hours, making, up to that time, a total of twenty-four-hours. I am careful that this raising of the temperature shall be gradual, and also to keep the steam spray in operation, the humidity rising to 90% by the time the full temperature of 150 F. is reached. I then gradually reduce the steam spray, and turning on more steam in the heating pipes gradually increase the temperature to about 160 F., and if the moisture is coming in suflicient volume from the wood, the humidity will rise to 95% or nearly to that point. If, when the steam spray is entirely cut off, the hygrodeik or other hygrometer employed still indicates that the humidity remains at this desired high point, it is an evidence that the necessary moisture to maintain the humidityis coming from the lumber; but if, on cuttin off the steam spray, the-humidity drops, it is an indication that sufficient moisture is not coming from the lumber to maintain the humidity desired, and I thereupon turn on the steam spray again and continue it for a short time until the high humidity is restored. There is no danger in continuing the admission of the steam spray at this time ialittle longer than is necessary, but it must not be stopped until the lumber is supplying from its ownmoisture sufiicient to maintain the high humidity specified. lhe gradual rise of the temperature from 150 F. to

160 F. and the described-gradual reductirln of the steam spray, together with the resu indicated, will usually occupy about twent four hours. As soon as this point is reached it will be found desirable to partly open the hinged valves 03 and dampers e controlling the inlet openings into the draft discharge flues. The various acids, such as tannic acid,

acetic acid, and other constituents which having issued from the wood in vaporous or gaseous form, are sufiiciently heavy to settle to the lower part of the kiln and below the lumber are thereby drawn off by the chimney exhaust and without drawing air-into the kiln. It is particularly desirable to thus remove these heavy vapors or gases, for the reason that if they remain in the chamber and in contact with the lower portion of the lumber, they may again, under varying conditions be re-absorbed by the lumber, to its injury. By providing ample space below the cars, and by providing the draft outlet for the kiln at the lower part thereof, I make certain that the draft-discharge flues shall remove these gases. The lighter volatilized oils which are not prejudicial to the lumber, will not settle below the lumber, but, in finely volatilized or gaseous form will remain in the steam chamber surrounding the lumber.

"Commencing also at the point where I find the lumber is freely giving off its own moisture in volume sufficient to maintain the high humidity,'I increase the admission of steam to'the heating pipes and run the temperature promptly reestablished by turning on the steam spray. The temperature should then be maintained at about 180 F. for about forty-eight la ours, making a total of five days. The hlnged valves d and dampers e may, during this period, be opened, more 'and more, but,'as before, the humidity must be maintained at the high point selected, or. as near the-re as ossible. If, during this period, the humidlty drops, it shows either that the lumber is sufiiciently dry, or that the valves 01 and dampers e are open too much. To ascertain whether the lumber is sufficiently dry, a test of a small piece of lumber taken out of the chamber should be promptly made, 'and while the test piece is being examined, it is advisable as a precautionary measure to turn on the steam spray to restore the humidity in the chamber. In any event, at the end of the fifth day (or at such earlier time as a drop in the humidity indicates as opportune, as just explained,) a test piece, as described, should be taken from the chamber. For this purpose, a number of small test pieces of lumber are provided, readily accessible throu h the door or a hand hole in the side 0 thekiln chamber where they have been subjected of course to the same conditions as has the main body of the lumber under treatment. If the test shows no shrinkage, this indicates that the kiln drying process is complete in the sense that the interior of the lumber is sufiiciently" dried. I then'shut off the steam from the heating coils and. from the spray-coil if the latter has been opened during the test, and open the air-inlet sides, thereby admittin air gradually, through the fiues s and s. thereby gradually reduce the temperature to from 100 F. to 120 F. (say 110 F.),' correspondingly cooling the lumber and carrying off by evaporation its surface moisture.

Under the conditions assumed, this cooling and surface evaporation should be accomplished in about twenty-four hours from the described cutting off of the steam from the heating coils, thus making a total of six days. The door of the kiln chamber is then opened and the car with its load of lumber is removed. The lumber is then preferably subjected to the action of the air for say forty-eight hours, until it is cooled down to atmospheric temperature, before sending it to the factory for use.

It will, of course, be apparent, to those skilled in the art, that if the stock treated has been still more thoroughly air dried in the first instance than has been assumed, it will go through the kiln in considerably less time, and stock of other dimensions, or of other varieties, in correspondingly different times. The skilled operator, however, in view of the foregoing description, and having in mind the fundamental necessity of maintaining the relative humidity in the kiln high and substantially constant until the interior of the stock, as determined by the test pieces, is thoroughly dry, will have no difficulty in applying the treatment to wood of any appropriate kind and condition met within practice.

lVhen the kiln is used as a progressive kiln in the sense that one or more cars carrying the lumber to be dried are admitted at the intake end of the kiln at the same time that a corresponding number of cars, completely dried, are removed at the out-take end of the kiln, the mode of operation, while genericsprayed with steam from the at a temperature of about 140 F. until the hygrodeik shows a relative humidity of ally the same in principle, is somewhat varied specifically, in accordance with the, varying conditions presented at successive parts of the kiln from the inlet to the outlet end thereof. In operating the kiln as a progressive kiln, the forward and smaller compartment shown at the left hand side of the drawing (Figs. 1 and 2), is separated from the main body portion of the kiln by dropping the curtain G and it is then to be used as a preliminary or tempering compartment before the lumber is transferred to the main body compartment beyond. When the lumber enters this tempering compartment, even though partially air dried, it is still comparatively green and should be pipes m, and

from 60% to 90% and over. The purpose of this preliminary spraying is to make the air as moist as possible even up to almost complete saturation, so that the effect of the .temperature to which it is subjected shall not to be case-harden the lumber, which would tend to occur, if the heated atmosphere were not of this high humidity. During the admission of the steam spray,- and throughout the operation of the kiln as a sible and the hinged valves d and dampers e of the tempering compartment are set half open. After the steam spray has continued for from fifteen to twenty minutes and when the hygrodei'k shows close to 90% humidity, the amount of steam entering the heating pipes is diminished, so as to maintain the humidity at approximately 90%. The temperature is then permitted to rise gradually, until, at the end of from twenty-four to forty-eight hours, it attains the same de ree that is contemplated at the entrance end of the main body of the kiln beyond the curtain. The relatively rapid rise in temperature in the first compartment or tempering compartment of the kiln makes it necessary to maintain the atmosphere therein at a very high degree of humidity. It is desirable, as

hereinbefore explained, that the moisture for this purpose should come from the lumber itself, in so far as that may be effected with-' out case-hardening the lumber, and, for the reason that in order that the drying of the lumber may proceed, the humidity of the atmosphere in which it is contained should be maintained as far as possible from the lumber and not from the steam admitted by the spray pipes, and to determine whether the lumber is giving ofl the necessary quantity of moisture, a'test may be readily made consisting in gradually reducing the amount of steam entering from the spray pipes and carefully noting whether the hygrodeik under these altered conditions continues to indicate substantially the same humidity.

In employing the apparatus as a progressive kiln, it is contemplated that the tempering compartment shall hold twice the number of cars that the kiln can dry daily when drying oak of one inch thickness. It will, therefore, be evident that by inserting in the tempering compartment daily as many cars as are taken out at the unloading end of the kiln, each car of lumber will be subjected to the tempering operation for a .period of forty-eight hours. For ash, basswood, poplar and all the soft woods, the time of treatment in the tempering kiln should be twenty-four hours, and, therefore, in withdrawing cars from the main compartment of the kiln, when these soft woods are being dried, it is necessary to withdraw as many cars from the main compartment of the kiln as are contained in the tempering kiln or compartment, so that the cars in the tempering kiln may be advanced into the main compartment. On the other hand, if the oak stock treated is of twice the cross sectional area of-that hereinbefore referred to, but one car should be removed on every second day. So also, in cases of mixed stock,

the cars should be detained in the tempering kiln for a period appropriate to the thicker and greener stock.

WVhen the forward car inthe tempering compartment, 2'. e., the car nearest the cur- 5 tain G, is ready to be advanced into the main Y compartment, the curtain is raised and the car is pushed forward. It is detained, however, after entering the main compartment, in that part of the main compartment which is immediately adjacent to the curtain, which, in the meantime, has again been closed, after the insertion of an additional car in the tempering compartment. The car that has been advanced into the main compartment finds itself in a relatively moist portion thereof where the humidity is high, because of the spraying in of the steam through the second pair of spraying pipes m Beyond these spraying pipes and near the outlet end of the main compartment, the relative humidity is considerably lower and the temperature higher, as will hereinafter more fully appear, so that, should the car that has been advanced into the main compartment 26 be at once moved to the extreme end thereof,

the lumber would become immediately casehardened, which, of course, is to be avoided. As the car enters the main compartment of the kiln, it is desirable to raise the hu- 30; midity at the unloading or discharge end of that compartment to about 60%, and this should be carefully attended to each time that the doors are opened and a car is forwarded. So also, as soon as the doors are closed, steam should be sprayed in through the pipes m so as to increase the humidity. Furthermore, when the cars are within two days of the discharge end, the humidity thereat should be reduced to thirty or forty W per cent., this being the percentage which it is desired to maintain at the discharge end; and, in fact, the humidity may in some instances be. decreased at the discharge end down to even 20%, when the kiln is operated by persons of experience. By the discharge end of the kiln, I mean that portion of the main compartment which is beyond the spray pipes m and which is not reached by any particular car until the interior of the lumber upon that car has been thoroughly dried; so that the function of this discharge portion of the kiln, when the kiln is being. operated as a progressive kiln, is merely to thoroughly dry the outer or exterior surfaces of the lumber, after the moisture has been expelled fromthe interior by the conditions prevailing in the preceding portions of the kiln.

In passing through the initial part of the main compartment of the kiln, the temperature is gradually increased up to' 160 F.

At these higher temperatures, the capacity of the atmosphere to take up moisture, per

unit volume of air, increases rapidly, and,

6 therefore, to maintain the atmosphere about the lumber at the desired point of relative high humidity, it is necessary, as the temperature rises, to increase the absolute quantity of moisture held by the more highly heated zones thereof along that portion of the main compartment corresponding to the location of the spray pipes m For instance, where the temperature along a' zone of that portion of the kiln corresponding to the location of the spray pipes m is 150 15 F., the humidity is maintained at and at the zone of said portion where the temperature is 160 F. the humidity is By thus raising the absolute humidity of the several zones along that portion of the kiln 8 where the interior of the wood is still giving off its moisture, I maintain substantial uniformity in. what is termed *the saturation deficit at said temperatures. In other words, inasmuch as the carrying power for moisture 35 of air at a temperature of 160 F. is greater than the carrying power of air at 150 F.,

I maintain the humidity of'the air zone which has been raised to 160 F., in the section of the kiln where the lumber is still 90 giving oif its interior moisture, at 95%, while maintaining the humidity of the corresponding zone of 150 F. at 90%, and, in so far as the tempering compartment of the kiln is concerned, maintaining 95 correspondingly lesser percentages of humidity because of the lesser temperatures prevailing therein. By this expedient, the

drawing or vaporating action exercised by the air upon the lumber, at these varying temperatures, is substantially uniform, in view of the fact that although the absolute humidity is different for each temperature,

the saturation deficit for air at the said temperatures and percentages of absolute humidity is substantially uniform. It will, of course, be understood, in this connection, that after a car has passed the region of j the spray pipes m and has, by that time given up its interior moisture, it is no longer necessary or'desirable to maintain the zone beyond that'point at a high percentage of humidity, inasmuch as the'only remaining function of the compartment is to dry the exterior surfaces of the lumber, which can then be done without injury to the lumber as a whole. a

In order to maintain the different degrees of humidity and the difi'erent temperatures desirable along the length of the kiln, the 1 2 0 several dampers 'or valves are appropriately adjusted, in accordance with the indications of the hygrodeik which may be inserted temporarily at various portions of the kiln. c For instance, should the humidity be too great at the unloading or discharge end of' ,the kiln, it maybe reduced by partially closing the dampers d and valves e at that endof the kiln and correspondingly opening the dampers and valves at the center of the kiln. So, also, should the humidity at the discharge end be too small, the dampers and valves at the center of the kiln may be partially closed and the dampers and valves at the end correspondingly opened, so as to cause a greater fiow of moist air toward the discharge end. In fact, it may be said generally that the greater degree of moisture will prevail in that portion of the kiln whose valves and dampers are so set as to give the greatest ease of escape. So also, to govern the draft in the draft discharge fiues 0, the amount of steam, at a given pressure, passing through the return bends f ma be increased or diminished by appropriately actuating the steam inlet valve and by setting the valves and dampers. In so far as the fresh air ducts s are concerned, I consider it desirable, as hereinbefore specified, that the dampers controlling these fresh air ducts be, as a rule, slightly opened, so as to operate the kiln, as before, under a regulated draft, which, at the center of the kiln, is comparatively slight, but which is of more considerable strength at the discharge or unloading end thereof.

To recapitulate; it will be seen that the application of a high temperature to lumber to be dried results in the case-hardening oft-he lumber if the heated atmosphere is not of sufficiently high humidity. In other words, the application of heated air of low humidity would promptly withdraw from the exterior of the wood a large quantity of moisture, withoutmaking material demands upon the moisture in the woods interior; and, as a consequence, the interior of the wood would remain moist and the exterior would become dry and case-hardened. To prevent this condition arising, it is necessary to have the heated air at a proper degree of humidity, so that its lifting power or capacity to take up moisture from the wood may be correspondingly limited. Air at a temperature of 120 F. and ata humidity of 65% has a liftglg capacity equal to "air at higher temperaturesand at higher per centages of humidity. Consequently, air at a temperature of 160 and with a humidity of 95% has practically the same lifting power for moisture or saturation deficit as air at, 120 F. and with a humidity of 65%. Accordingly, air of these respective tem peratures and humidities may be reckoned in each case as air of high humidity for the purposes of the invention. So, also, air at intermediate temperatures between 120 and 160 and at intermediate absolute humidities may all be reckoned as of 'high ployment of air at a temperature of 120 F. and at a humidity of 65%, up to air at a temperature of 160 F. and at a humidity of 95%. The higher the temperature, the quicker the drying operation, but practically the same relatively high humidity and practically the same saturation deficit must prevail, inorder to secure the advantages of the process which consists in thus driving out the moisture from the interior of the lumber untilit is thoroughly dried, and, in the meantime, maintaining the exterior of the lumber in a soft and moist condition so that it will not become casehardened. Eventually, however, the exterior of the lumber. must also be dried in order that the work of drying the lumber as a whole may be completed. Consequently, near the end of-the operation, if the drying is carried on in a box kiln, the humidity is permitted. to

drop, and the temperature of the air may be somewhat raised, without detriment; inasmuch as at this stage of the operation, the interior of the wood is already dried and, therefore, there remains merely the drying of the exterior. kiln, the proper conditions for the drying out of the interior of the lumber, without case-hardening, are preserved by the employment of heated air of high humidity, which air is increased in temperature up to themaximum of 160 F.; and, when the interior, of the lumber has thus been dried and the cars are approaching the unloading end of the kiln, it merely remains to dry the exterior surfaces, which can be speedily accomplished by lowering the humidity at the unloading end and raising the temperature somewhat.

The provision of the. stack fines at different points along the kiln is for the purpose of changing the humidity and temperature .at different parts of the kiln, and particularly to prevent either a drop or a rise of humidity at the unloading end of the kiln beyond what is contemplated by the invention.

What I claim is 1. The method of drying lumber, which consists in subjecting it to heat in an inclosed space, and protecting its exterior from case-hardening during the period that the moisture -is being expelled from its interior, by maintaining about it an atmosphere of practically uniform saturation deficit but of high humidity, until the interior'pf the lumber is thoroughly dry; substantially as described. 1

2. The method of drying lumber, which consists in subjecting it to heat in an in- So also, in the continuous closed space, and protecting its exterior from practically uniform saturation deficit but of high humidity, until the interior of the lumber is thoroughly dry and preventing undue excess of humidity by keeping the kiln during said period under a regulable draft, substantially as described.

.3. Themethod of drying lumber, which consists in subjecting it to heat in an inclosed space, and protecting its exterior from case-hardening during the period that the moisture is being expelled from its interior, by establishing by the admissionof steam, a protective atmosphere of highhumidity about the lumber, and diminishing or increasing the quantity of steam admitted in proportion as the moisture expelled from the lumber increases or diminishes, thus maintaining constant high humidity until the interior of the lumber is thoroughly dry; substantially as described.

4. The method of drying lumber, which consists in subjecting it to heat in an in-v closed space and protecting its exterior from case-hardening during the period that the moisture is being expelled from its interior by establishing-by the admission of steam a protective atmosphere of high humidity about the lumber, gradually diminishing the quantity of steam admitted in proportion as the moisture expelled from the lumberincreases, and finally cutting off the admission of steam and maintaining the high humidity by the moisture from the lumber alone until its interior is thoroughly dry; substantially as described. Y

5. The method of drying lumber, which consists in preliminarily subjecting it to heat, in an inclosed space, in the presence of steam,

7 thereby surrounding the lumber during this preliminary stage by a heated atmosphere containing a high percentage of moisture until the lumber is freely giving off its contained moisture in the form of vapor, thereafter continuing to drive off the moisture from the lumber by the further application of heat, and, as the lumber adds its moisture to the atmosphere within the inclosed space, maintaining the humidity substantially constant until the interior of the lumber is thoroughly dry; substantially as described.

6. The method of drying lumber, which consists in subjecting it to heat in an inclosed space and protecting its exterior from case-hardening during the period that the moisture is being expelled from its interior by maintaining about it an atmosphere of .by maintaining the vhumidity of the atmosphere in said space at a, practically uniform saturation deficit, and gradually increasing the temperature until the interior of the lumber is' thoroughly dry, without materially varying the saturation deficit of the inclosed drying atmosphere; substantiallyas described.

8. The method of drying lumber, which consists in inclosing the lumber in asu-bstantially air tight space, admitting steam thereto until the humidity in said space is raised to a predetermined point of saturation deficit, anduntil the lumber attains the temperature of the surrounding medium, then gradually raising the temperature still further whlle gradually'reducing and finally interrupting the admission of steam, and thereafter gradually raising the temperature still further, while maintaining the medium, during the successive increments of temperature at substantially the same predetermined point of saturation deficit until the interior ofthe lumber is thoroughly dry; substantially as described.

9. The method of drying lumber, which consists in subjecting it to heat in an inclosed space for the purpose of driving off its interior moisture, and protecting it against injury during the moisture-expelling period by maintaining about it an atmosphere kept constantly charged with high humidity until the interior of the lumber is thoroughly dry,

and, during the operation, drawing 011' the heavy acid vapors or gases that have been expelled from the lumber and that have settled because of theirhigher specific gravity, the entrance of air being excluded during the removal of said heavy acid vapors or gases; substantially as described.

' In testimony wherof I afiix my signature, in presence of two witnesses.

, ALLEN D. LINN. Witnesses:

A. C. DENIsoN, MARY S. TOOKER.

Patent No. 1,005,248, granted October 10, 1911, upon the application ;of Allen D; Linn, of Grand Rapids, Michigan, for an It is hereby certified that in Letters improvement in Drying Lumber, an error appears in the printed specification requiring correction as follows: Page 3, line 125, for the word sides read slides, and that the said Letters Patent should. he read yvith this correction therein that the same may conform to the record of the case the Patent Oflice.

Signed and sealed this 7th day of November, A. D., 1911.

' E. B. MOORE,

Commihsoner of Patents.

[SEAL.] 

